Ancient bones tell new story of how medieval Europe was formed

Novel statistical tool reveals Roman Empire’s genetic legacy more complex than historians thought

LONDON — Like examining the growth rings of an ancient tree, scientists have developed a new way to analyze the “twigs” of human genetic family trees, revealing previously hidden patterns of migration across early medieval Europe. Their findings overturn long-held assumptions about population movements during the twilight of the Roman Empire and the dawn of the Viking Age.

A team of international researchers, led by Leo Speidel and Pontus Skoglund at the Francis Crick Institute, developed an innovative analytical approach called Twigstats that dramatically improves our ability to track ancient population movements through DNA analysis. Their study, published in Nature, represents a significant advance in our ability to detect subtle genetic changes in ancient populations, offering unprecedented insight into European history from 500 BCE to 1000 CE.

“We already have reliable statistical tools to compare the genetics between groups of people who are genetically very different, like hunter-gatherers and early farmers, but robust analyses of finer-scale population changes, like the migrations we reveal in this paper, have largely been obscured until now,” explains Speidel, who is now a group leader at RIKEN, Japan, in a statement.

The investigation examined 1,556 ancient whole genomes from across Europe, representing one of the largest studies of its kind. What emerged was a complex tapestry of human migration and interaction that sometimes aligned with historical records and occasionally revealed surprising new patterns.

During the first half of the first millennium CE, the researchers identified at least two distinct streams of Scandinavian-related ancestry expanding across western, central, and eastern Europe. This finding provides genetic evidence for historical accounts of population movements during the decline of the Roman Empire, though the exact nature and scale of these migrations have long been debated by historians.

A particularly intriguing discovery emerged from Roman-era Britain. In York (Roman Eboracum) during the 2nd-4th century, researchers identified an individual who may have been a Roman soldier or slave gladiator carrying 25% early Iron Age Scandinavian Peninsula-related ancestry. This finding demonstrates that people with Scandinavian ancestry were present in Britain well before the traditionally recognized Anglo-Saxon and Viking periods that began in the 5th century CE.

One of the study’s most significant discoveries concerned the Viking Age. Around 800 CE, the researchers documented a “major ancestry influx” in Scandinavia when a large proportion of Viking Age individuals swiftly carried ancestry from groups related to central Europe, a heritage not seen in individuals from the early Iron Age. This suggests a significant population movement into Scandinavia before the Viking Age that had been previously unknown.

“Historical sources indicate that migration played some role in the massive restructuring of the human landscape of western Eurasia in the second half of the first millennium AD which first created the outlines of a politically and culturally recognizable Europe, but the nature, scale and even the trajectories of the movements have always been hotly disputed,” explains co-author Peter Heather, Professor of Medieval History at King’s College London.

The study revealed fascinating details about migration patterns matching linguistic evolution. The two main zones of migration and interaction mirror the three main branches of Germanic languages: one that remained in Scandinavia, another that became extinct, and a third that evolved into modern-day German and English.

In Viking Age mass graves discovered in Britain, researchers found genetic evidence supporting historical accounts. The remains of men who died violently showed genetic links to Scandinavia, suggesting they may have been executed members of Viking raiding parties. Additionally, the team identified Viking Age individuals in present-day Ukraine and Russia who carried ancestry from present-day Sweden, while individuals in Britain showed ancestry from present-day Denmark.

“The goal was a data analysis method that would provide a sharper lens for fine-scale genetic history,” says Pontus Skoglund, Group Leader of the Ancient Genomics Laboratory at the Crick and senior author of the study. “Questions that wouldn’t have been possible to answer before are now within reach to us, so we now need to grow the record of ancient whole-genome sequences.”

The innovative Twigstats method works by analyzing genetic mutations shared between individuals. Since DNA is inherited through ancestors, shared mutations serve as markers of relatedness. By focusing specifically on more recent mutations, the method reveals connections between people who lived closer together in time, providing unprecedented resolution for studying historical population movements.

“Twigstats allows us to see what we couldn’t before,” notes Speidel, “in this case migrations all across Europe originating in the north of Europe in the Iron Age, and then back into Scandinavia before the Viking Age. Our new method can be applied to other populations across the world and hopefully reveal more missing pieces of the puzzle.”

From the Roman gladiator with Scandinavian ancestry to the pre-Viking influx that transformed northern Europe, this research reveals that our ancestors were far more mobile and interconnected than previously thought. As new genetic analysis tools continue to emerge, we may find that many more surprises await us in the twisted branches of Europe’s family tree.